Base station and radio terminal

ABSTRACT

A base station according to one embodiment includes: a transmitter configured to transmit a synchronization signal in a cell using a predetermined subcarrier spacing, the cell being managed by the base station; and a controller configured to arrange, based on the predetermined subcarrier spacing, the synchronization signal in a plurality of discrete subcarriers not continuous in a frequency direction.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation based on PCT Application No.PCT/JP2017/001185 filed on Jan. 16, 2017, which claims the benefit ofJapanese Patent Application No. 2016-018856 (filed on Feb. 3, 2016). Thecontent of which is incorporated by reference herein in their entirety.

FIELD

The present invention relates to a base station and a radio terminalused in a mobile communication system.

BACKGROUND

In recent years, research on a technology for the fifth generation (5G)mobile communication system is underway. One such known technology isbased on OFDM (Orthogonal Frequency Division Multiple), where afrequency band and/or a radio parameter depending on a usage is scalable(variable). For example, in the existing LTE (Long Term Evolution), asubcarrier spacing (SS) is basically fixed at 15 kHz, and in a highfrequency band, the subcarrier spacing is considered to be widened.

SUMMARY

A base station according to one embodiment comprises a transmitterconfigured to transmit a synchronization signal in a cell using apredetermined subcarrier spacing, the cell being managed by the basestation; and a controller configured to arrange, based on thepredetermined subcarrier spacing, the synchronization signal in aplurality of discrete subcarriers not continuous in a frequencydirection.

A base station according to one embodiment comprises a transmitterconfigured to transmit a synchronization signal in a cell using apredetermined subcarrier spacing, the cell being managed by the basestation; and a controller configured to apply a subcarrier spacingdifferent from the predetermined subcarrier spacing to a time locationfor transmitting the synchronization signal.

A radio terminal according to one embodiment comprises a receiverconfigured to receive a synchronization signal of a cell of a basestation; and a controller configured to perform a reception process ofthe synchronization signal by using a previously set specifiedsubcarrier spacing, irrespective of a subcarrier spacing of the cell.

A base station according to one embodiment comprises a transmitterconfigured to transmit, in a first cell, subcarrier spacing informationto a radio terminal. The subcarrier spacing information indicates asubcarrier spacing of a second cell different from the first cell.

A radio terminal according to one embodiment comprises a receiverconfigured to receive, in the first cell, subcarrier spacing informationfrom a base station, where the subcarrier spacing information indicatesa subcarrier spacing of a second cell different from the first cell; anda controller configured to recognize, based on the subcarrier spacinginformation, the subcarrier spacing of the second cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an LTE system.

FIG. 2 is a diagram illustrating a protocol stack of a radio interfacein the LTE system.

FIG. 3 is a diagram illustrating a configuration of a radio frame usedin the LTE system.

FIG. 4 is a diagram illustrating a configuration of a UE (radioterminal).

FIG. 5 is a diagram illustrating a configuration of an eNB (basestation).

FIG. 6 is a chart illustrating an OFDM signal waveform.

FIG. 7 is a diagram illustrating an example of an assumed scenarioaccording to first to third embodiments.

FIGS. 8(a) and 8(b) are diagrams each illustrating an example of anarrangement of a synchronization signal.

FIG. 9 is a diagram illustrating an operation example of the eNBaccording to the first embodiment.

FIG. 10 is a diagram illustrating an operation example of the eNBaccording to the second embodiment.

FIG. 11 is a diagram illustrating an operation example of the eNB andthe UE according to the third embodiment.

DESCRIPTION OF THE EMBODIMENT Overview of Embodiment

A radio terminal performs a cell search to search a synchronizationsignal of a cell to establish a synchronization with the cell for cellidentification. Therefore, if a reception process of the synchronizationsignal (that is, a synchronization process) is not successful, the radioterminal cannot be synchronized with the cell nor identify the cell.

Here, if a case is assumed where the subcarrier spacing is scalable, thesubcarrier spacing of the synchronization signal may also be scalable.In this case, the radio terminal may need to use all the possiblesubcarrier spacings to perform the synchronization process. However,such a method is not preferable from a viewpoint of a process load ofthe radio terminal.

Accordingly, an object of an embodiment is to provide a base station anda radio terminal capable of suppressing an increase of a process load ofa radio terminal even if a subcarrier spacing is scalable.

A base station according to a first embodiment comprises a transmitterconfigured to transmit a synchronization signal in a cell using apredetermined subcarrier spacing, the cell being managed by the basestation; and a controller configured to arrange, based on thepredetermined subcarrier spacing, the synchronization signal in aplurality of discrete subcarriers not continuous in a frequencydirection.

In the first embodiment, the controller may arrange the synchronizationsignal in the plurality of discrete subcarriers, if the predeterminedsubcarrier spacing is narrower than a previously set specifiedsubcarrier spacing. In the plurality of discrete subcarriers, a spacingbetween the two adjacent discrete subcarriers is equal to the specifiedsubcarrier spacing.

In the first embodiment, the specified subcarrier spacing is may besubcarrier spacing used by a radio terminal for a reception process ofthe synchronization signal.

In the first embodiment, the synchronization signal may include a signalsequence indicating the predetermined subcarrier spacing.

A base station according to a second embodiment comprises a transmitterconfigured to transmit a synchronization signal in a cell using apredetermined subcarrier spacing, the cell being managed by the basestation; and a controller configured to apply a subcarrier spacingdifferent from the predetermined subcarrier spacing to a time locationfor transmitting the synchronization signal.

In the second embodiment, if the predetermined subcarrier spacing isdifferent from a previously set specified subcarrier spacing, thecontroller may apply the specified subcarrier spacing to a time locationfor transmitting the synchronization signal.

In the second embodiment, the specified subcarrier spacing may be asubcarrier spacing used by a radio terminal for a reception process ofthe synchronization signal.

In the second embodiment, the synchronization signal may include asignal sequence indicating the predetermined subcarrier spacing.

A radio terminal according to the first and second embodiment comprisesa receiver configured to receive a synchronization signal of a cell of abase station; and a controller configured to perform a reception processof the synchronization signal by using a previously set specifiedsubcarrier spacing, irrespective of a subcarrier spacing of the cell.

In the first and second embodiments, the synchronization signal mayinclude a signal sequence indicating a subcarrier spacing of the cell.The controller may recognize, based on the signal sequence, thesubcarrier spacing of the cell.

A base station according to a third embodiment comprises a transmitterconfigured to transmit, in a first cell, subcarrier spacing informationto a radio terminal. The subcarrier spacing information indicates asubcarrier spacing of a second cell different from the first cell.

In the third embodiment, the first cell may be a primary cell of theradio terminal. The second cell may be a secondary cell of the radioterminal.

A radio terminal according to the third embodiment comprises a receiverconfigured to receive, in the first cell, subcarrier spacing informationfrom a base station, where the subcarrier spacing information indicatesa subcarrier spacing of a second cell different from the first cell; anda controller configured to recognize, based on the subcarrier spacinginformation, the subcarrier spacing of the second cell.

In the third embodiment, the controller may perform a reception processof a synchronization signal of the second cell by using the recognizedsubcarrier spacing.

[Mobile Communication System]

The configuration of the mobile communication system according to theembodiment will be described. In the embodiment, it is assumed that a 5Gmobile communication system is a system that has evolved the LTE system.

(1) Configuration of system

FIG. 1 is a diagram illustrating a configuration of an LTE system. Asillustrated in FIG. 1, the LTE system includes a User Equipment (UE)100, an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) 10, andan Evolved Packet Core (EPC) 20. The E-UTRAN 10 and the EPC 20constitute a network of the LTE system.

The UE 100 corresponds to a radio terminal. The UE 100 is a mobilecommunication terminal. The UE 100 performs radio communication with acell (serving cell). The configuration of the UE 100 will be describedlater.

The E-UTRAN 10 corresponds to a radio access network. The E-UTRAN 10includes an evolved Node-B (eNB) 200. The eNB 200 corresponds to a basestation. The eNBs 200 are connected to each other via an X2 interface.The configuration of the eNB 200 will be described later.

The eNB 200 manages one or a plurality of cells. The eNB 200 performsradio communication with the UE 100 that has established connection withcells managed by the eNB 200. The eNB 200 has a radio resourcemanagement (RRM) function, a routing function of user data (hereinafter,simply referred to as “data”), a measurement control function formobility control and scheduling, and the like. The “cell” is used as aterm indicating the minimum unit of a radio communication area. The“cell” is also used as a term indicating a function of performing radiocommunication with the UE 100.

The EPC 20 corresponds to a core network. The EPC 20 includes an MME(Mobility Management Entity)/S-GW (Serving-Gateway) 300. The MMEperforms various mobility control and the like for the UE 100. The S-GWperforms data transfer control. The MME/S-GW 300 is connected to the eNB200 via an S1 interface. The E-UTRAN 10 and the EPC 20 constitute anetwork.

FIG. 2 is a diagram illustrating protocol stack of a radio interface inthe LTE system. As illustrated in FIG. 2, a radio interface protocol isseparated into first to third layers of an Open Systems Interconnection(OSI) reference model. The first layer is a physical (PHY) layer. Thesecond layer includes a Medium Access Control (MAC) layer, a Radio LinkControl (RLC) layer, and a Packet Data Convergence Protocol (PDCP)layer. The third layer includes a Radio Resource Control (RRC) layer.

The physical layer, the MAC layer, the RLC layer, the PDCP layer, andthe RRC layer constitute an AS (Access Stratum) entity 100 a. The upperlayer entity 100 b is positioned higher than the AS entity 100 a. Theupper layer entity 100 b includes an NAS (Non-Access Stratum) layer. Theupper layer entity 100 b may further include an application layer or thelike.

The physical layer performs encoding/decoding, modulation/demodulation,antenna mapping/demapping, and resource mapping/demapping. Between thephysical layer of the UE 100 and the physical layer of the eNB 200, dataand control signal are transferred via a physical channel.

The MAC layer performs data priority control, retransmission processingusing a hybrid automatic repeat request (ARQ) (HARQ), a random accessprocedure, and the like. Between the MAC layer of the UE 100 and the MAClayer of the eNB 200, data and control signal are transferred via atransport channel. The MAC layer of the eNB 200 includes a scheduler.The scheduler decides a transport format (transport block size andmodulation and coding schemes (MCS)) of uplink and downlink, and aresource block to be allocated to the UE 100.

The RLC layer transfers data to an RLC layer on a reception side usingthe functions of the MAC layer and the physical layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data and controlinformation are transferred via a logical channel.

The PDCP layer performs header compression/decompression, andencryption/decryption.

The RRC layer is defined only in a control plane handling controlsignal. Between the RRC layer of the UE 100 and the RRC layer of the eNB200, signaling (RRC signaling) for various configurations aretransferred. The RRC layer controls the logical channel, the transportchannel, and the physical channel in response to establishment,re-establishment, and release of a radio bearer. If there is connection(RRC connection) between the RRC of the UE 100 and the RRC of the eNB200, the UE 100 is in an RRC connected mode. If there is not aconnection (RRC connection) between the RRC of the UE 100 and the RRC ofthe eNB 200, the UE 100 is in an RRC idle mode.

A non-access stratum (NAS) layer located above the RRC layer performs,for example, session management, mobility management, and the like.

FIG. 3 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, Orthogonal Frequency Division Multiple Access(OFDMA) is applied to downlink, Single Carrier Frequency DivisionMultiple Access (SC-FDMA) is applied to uplink, respectively.

As illustrated in FIG. 3, a radio frame is constituted by ten subframesarranged in a time direction. Each subframe is constituted by two slotsarranged in the time direction. The length of each subframe is 1 ms, andthe length of each slot is 0.5 ms. Each subframe includes a plurality ofresource blocks (RBs) in a frequency direction. Each subframe includes aplurality of symbols in the time direction. Each resource block includesa plurality of subcarriers in the frequency direction. One resourceelement (RE) is constituted by one symbol and one subcarrier. Among theradio resources (time/frequency resources) allocated to the UE 100,frequency resources can be specified by resource blocks, and timeresources can be specified by subframes (or slots).

(2) Configuration of Radio Terminal

FIG. 4 is a diagram illustrating configuration of the UE 100 (radioterminal). As illustrated in FIG. 4, the UE 100 includes a receiver 110,a transmitter 120, and a controller 130.

The receiver 110 performs various types of reception under the controlof the controller 130. The receiver 110 includes an antenna and areceiving device. The receiving device converts a radio signal receivedby the antenna, into a baseband signal (reception signal). The receivingdevice outputs the baseband signal to the controller 130.

The transmitter 120 performs various types of transmission under thecontrol of the controller 130. The transmitter 120 includes an antennaand a transmission device. The transmission device converts a basebandsignal (transmission signal) output by the controller 130, into a radiosignal. The transmission device transmits the radio signal from theantenna.

The controller 130 performs various types of control in the UE 100. Thecontroller 130 includes a processor and a memory. The memory stores aprogram to be executed by the processor, and information to be used inprocessing performed by the processor. The processor may include abaseband processor and a central processing unit (CPU). The basebandprocessor performs modulation/demodulation and encoding/decoding of abaseband signal, and the like. The CPU executes programs stored in thememory, to perform various types of processing. The processor mayinclude a codec that performs encoding/decoding of an audio/videosignal. The processor executes the above-described various processes andvarious processes to be described later.

(3) Configuration of Base Station

FIG. 5 is a diagram illustrating configuration of the eNB 200 (basestation). As illustrated in FIG. 5, the eNB 200 includes a transmitter210, a receiver 220, a controller 230, and a backhaul communication unit240.

The transmitter 210 performs various types of transmission under thecontrol of the controller 230. The transmitter 210 includes an antennaand a transmission device. The transmission device converts a basebandsignal (transmission signal) output by the controller 230, into a radiosignal. The transmission device transmits the radio signal from theantenna.

The receiver 220 performs various types of reception under the controlof the controller 230. The receiver 220 includes an antenna and areceiving device. The receiving device converts a radio signal receivedby the antenna, into a baseband signal (reception signal). The receivingdevice outputs the baseband signal to the controller 230.

The controller 230 performs various types of control in the eNB 200. Thecontroller 230 includes a processor and a memory. The memory stores aprogram to be executed by the processor, and information to be used inprocessing performed by the processor. The processor may include abaseband processor and a central processing unit (CPU). The basebandprocessor performs modulation/demodulation and encoding/decoding of abaseband signal, and the like. The CPU executes programs stored in thememory, to perform various types of processing. The processor executesthe processor to be described later.

The backhaul communication unit 240 is connected with an adjacent eNB200 via the X2 interface. The backhaul communication unit 240 isconnected with the MME/S-GW 300 via the S1 interface. The backhaulcommunication unit 240 is used for communication performed on the X2interface, communication performed on the S1 interface, and the like.

First Embodiment

A first embodiment will be described, below.

(1) Assumed Scenario

In the first embodiment, a scenario is assumed where the subcarrierspacing (SS) is scalable in an OFDM-based signal transmission.

FIG. 6 is a chart illustrating an OFDM signal waveform. As illustratedin FIG. 6, the OFDM transmission is a type of a multicarrier modulationscheme where data is distributed to a plurality of orthogonalsubcarriers and the data is transmitted in parallel in a frequencydirection. The subcarrier spacing indicates a spacing between twoadjacent subcarriers. Further, not only the subcarrier spacing but alsoa system bandwidth and/or OFDM symbol length may be scalable. Forexample, the subcarrier spacing may be widened, and the OFDM symbollength may be shortened.

FIG. 7 is a diagram illustrating an example of an assumed scenarioaccording to the first embodiment. As illustrated in FIG. 7, an eNB200-1 manages a cell 1, an eNB 200-2 manages a cell 2, and an eNB 200-3manages a cell 3. Here, an example is provided where one eNB 200 managesone cell, however, one eNB 200 may manage a plurality of cells.

In the first embodiment, a case is primarily assumed where depending onan operation environment of each cell, a different subcarrier spacing isapplied. In the example of FIG. 7, the cell 1 is a macro cell where asubcarrier spacing of 15 kHz is applied. Further, the cell 2 is a smallcell for an outdoor use, where a subcarrier spacing of 30 kHz isapplied. The cell 3 is a small cell for an indoor use, where asubcarrier spacing of 60 kHz is applied.

FIGS. 8(a) and 8(b) are diagrams each illustrating an example of anarrangement of a synchronization signal. It is noted that in a resourcegrid illustrated in FIGS. 8(a) and 8(b) and subsequent figures, onesection in a vertical direction indicates one subcarrier, and onesection in a lateral direction indicates one OFDM symbol.

As illustrated in FIG. 8(a), in an existing LTE system, the subcarrierspacing (SS) is 15 kHz. The synchronization signal is arranged, in thefrequency direction, in six resource blocks (6RBs) in the center of thesystem bandwidth. Specifically, the synchronization signal is arrangedin a plurality of continuous subcarriers. In a time direction, thesynchronization signal is arranged in a previously set time location. Inthe existing LTE system, the synchronization signal includes a primarysynchronization signal arranged in the last OFDM symbol of a first-halfslot for each five subframes, and a secondary synchronization signalarranged in the next-to-last (that is, immediately before the primarysynchronization signal) OFDM symbol in the same slot as the primarysynchronization signal. It is noted that when the synchronization signalis applied to the 5G system, an arrangement similar to that in theexisting LTE system may not always be established.

By performing a cell search for searching the synchronization signal ofthe cell, the UE 100 establishes the synchronization with the cell forcell identification. Therefore, if a reception process of thesynchronization signal (that is, a synchronization process) is notsuccessful, the UE 100 cannot be synchronized with the cell nor identifythe cell.

As illustrated in FIG. 8(b), when the subcarrier spacing is scalable,the subcarrier spacing (SS) is 30 kHz, for example. As compared withFIG. 8(a), the subcarrier spacing is doubled, and the OFDM symbol lengthis one half. If the subcarrier spacing is scalable, the subcarrierspacing of the synchronization signal may also be scalable. Therefore,the UE 100 may need to perform a synchronization process by using all ofthe possible subcarrier spacings. However, such a method is notpreferable from a viewpoint of a process load of the UE 100.

(2) Operation According to First Embodiment

The eNB 200 according to the first embodiment includes a transmitter 210configured to transmit a synchronization signal in a cell using apredetermined subcarrier spacing, the cell being managed by the eNB 200,and a controller 230 configured to arrange, based on the predeterminedsubcarrier spacing, the synchronization signal in a plurality ofsubcarriers (hereinafter, “discrete subcarriers”) not continuous in thefrequency direction. The time location to arrange the synchronizationsignal is previously set. That is, the eNB 200 may transmit thesynchronization signal on a symbol arranged in the same time location,irrespective of the subcarrier spacing.

In the first embodiment, the controller 230 arranges the synchronizationsignal in the discrete subcarrier, if the predetermined subcarrierspacing is narrower than a previously set specified subcarrier spacing.Specifically, in a scenario where there are a plurality of cellsdifferent in subcarrier spacing, the widest subcarrier spacing ispreviously set as the specified subcarrier spacing. Further, in thediscrete subcarrier, a spacing between the two adjacent discretesubcarriers is equal to the specified subcarrier spacing. The specifiedsubcarrier spacing is a subcarrier spacing used by the UE 100 for thereception process of the synchronization signal. The synchronizationsignal includes a signal sequence (code sequence) indicating apredetermined subcarrier spacing.

The UE 100 according to the first embodiment includes a receiver 110configured to receive the synchronization signal of the eNB 200; and acontroller 130 configured to perform the reception process of thesynchronization signal by using the previously set specified subcarrierspacing, irrespective of the subcarrier spacing of the cell. Thecontroller 130 may perform the reception process of the synchronizationsignal in a previously set time location. The controller 130 recognizes,based on the signal sequence of the received synchronization signal, thesubcarrier spacing of the cell from which the synchronization signal istransmitted.

FIG. 9 is a diagram illustrating an operation example of the eNB 200according to the first embodiment. Here, a case is assumed where thereare a cell 1 with the subcarrier spacing (SS) being 15 kHz and a cell 2with the subcarrier spacing (SS) being 30 kHz. The cell 1 and the cell 2may be managed by the same eNB 200, and may be managed by a differenteNB 200. In FIG. 9, an example is illustrated where the cell 1 ismanaged by the eNB 200-1, and the cell 2 is managed by the eNB 200-2.

The eNB 200-1 transmits a synchronization signal 1, in the cell 1 usingthe subcarrier spacing of 15 kHz. The synchronization signal 1 includesa signal sequence 1 indicating 15 kHz. The eNB 200-2 transmits asynchronization signal 2, in the cell 2 using the subcarrier spacing of30 Hz. The synchronization signal 2 includes a signal sequence 2indicating 30 kHz. In the example of FIG. 9, the subcarrier spacing of30 Hz corresponds to the previously set specified subcarrier spacing.

The eNB 200-1 arranges the synchronization signal 1 in the discretesubcarrier because the subcarrier spacing of the cell 1 is narrower thanthe specified subcarrier spacing. On the other hand, the eNB 200-2arranges the synchronization signal 2 in a plurality of subcarriers(continuous subcarriers) continuous in the frequency direction. The eNB200-1 and the eNB 200-2 arrange the synchronization signals 1, 2 in atime location at an equal time location (predetermined symbol interval).

In the discrete subcarrier where the eNB 200-1 arranges thesynchronization signal 1, the spacing between the two adjacent discretesubcarriers is equal to the specified subcarrier spacing. Specifically,the eNB 200-1 arranges the synchronization signal 1 with a ratio of onesubcarrier in every two subcarriers. As a result, the spacing of thesubcarrier where the synchronization signal 1 is arranged is equal to 30kHz (specified subcarrier spacing).

The UE 100 uses 30 kHz or previously set specified subcarrier spacing toperform the reception process of the synchronization signal(synchronization process) at the previously set time location.Accordingly, with a similar signal process, the UE 100 can receive anddemodulate the synchronization signal 1 of the cell 1 and thesynchronization signal 2 of the cell 2. In other words, the UE 100 canreceive and demodulate also the synchronization signal 1 of the cell 1,with the signal process similar to the signal process used for thesynchronization signal 2 of the cell 2.

Then, the UE 100 recognizes, based on the signal sequence of thereceived synchronization signal, the subcarrier spacing of the cell. Forexample, the UE 100 recognizes, based on the signal sequence 1 of thesynchronization signal 1 received from the cell 1, that the subcarrierspacing of the cell 1 is 15 kHz. Further, the UE 100 recognizes, basedon the signal sequence 2 of the synchronization signal 2 received fromthe cell 2, that the subcarrier spacing of the cell 2 is 30 kHz.

After recognizing the subcarrier spacing of the cell, the UE 100performs the reception process of another signal by using the subcarrierspacing. The other signal is, for example, a cell-specific referencesignal and system information (a master information block, a systeminformation blocks or the like). The UE 100 can start communication withthe cell by receiving these signals.

(3) Summary of First Embodiment

According to the first embodiment, the eNB 200-1 arranges thesynchronization signal 1 in the discrete subcarrier so that thesubcarrier spacing of the synchronization signal 1 is the specifiedsubcarrier spacing (30 kHz). As a result, the UE 100 can perform thesynchronization process with the cell 1 by using the specifiedsubcarrier spacing (30 kHz). That is, with a standardizedsynchronization process, the UE 100 can receive the synchronizationsignal 1 of the cell 1 and the synchronization signal 2 of the cell 2cell 1. Therefore, even if the subcarrier spacing is scalable, it ispossible to suppress an increase of a process load of the UE 100.

(4) First Modification of First Embodiment

In the first embodiment described above, the example was described whereif there are the cell 1 with the subcarrier spacing (SS) being 15 kHzand the cell 2 with the subcarrier spacing (SS) being 30 kHz, thesubcarrier spacing of 30 kHz is previously defined as the specifiedsubcarrier spacing. However, in a case where there are the cell 1 withthe subcarrier spacing (SS) being 15 kHz, the cell 2 with the subcarrierspacing (SS) being 30 kHz, and the cell 3 with the subcarrier spacing(SS) being 60 kHz, the subcarrier spacing of 60 kHz may be previouslydefined as the specified subcarrier spacing.

(5) Second Modification of First Embodiment

In the first embodiment described above, a setting method of thespecified subcarrier spacing was not particularly mentioned. However,the specified subcarrier spacing may be previously defined by a systemspecification. Similarly, the time location where the synchronizationsignal is arranged may also be previously defined.

Alternatively, the specified subcarrier spacing may be set and updatedto the UE 100 and the eNB 200 by the signaling from the core network orOAM (Operations Administration and Maintenance). Similarly, the timelocation where the synchronization signal is arranged may also be setand updated to the UE 100 and the eNB 200 by the signaling from the corenetwork or the OAM.

Second Embodiment

A second embodiment will be described while focusing on a differencefrom the first embodiment, below. An assumed scenario according to thesecond embodiment is similar to the assumed scenario according to thefirst embodiment.

(1) Operation According to Second Embodiment

The eNB 200 according to the second embodiment includes, a transmitter210 configured to transmit a synchronization signal in the cell using apredetermined subcarrier spacing, the cell being managed by the eNB 200,and a controller 230 configured to apply a subcarrier spacing differentfrom the predetermined subcarrier spacing to a time location fortransmitting the synchronization signal. In other words, in the secondembodiment, the eNB 200 applies the subcarrier spacing different fromanother time location (that is, a subcarrier for transmitting data),only to the time location of the synchronization signal. Specifically,if the predetermined subcarrier spacing is different from the previouslyset specified subcarrier spacing, the controller 230 applies thespecified subcarrier spacing to the time location for transmitting thesynchronization signal. Further, similarly to the first embodiment, thetime location where the synchronization signal is to be arranged may bepreviously set. The synchronization signal includes the signal sequenceindicating the predetermined subcarrier spacing.

A method of defining and setting the specified subcarrier spacing issimilar to those in the first embodiment and the modification thereof.That is, the specified subcarrier spacing is the subcarrier spacing usedby the UE 100 for the reception process of the synchronization signal.An operation of the UE 100 is similar to that in the first embodiment.

FIG. 10 is a diagram illustrating an operation example of the eNB 200according to the second embodiment. Here, a case is illustrated where ifthere is the cell 2 with the subcarrier spacing (SS) being 30 kHz, thespecified subcarrier spacing is 15 kHz. The cell 2 is managed by the eNB200-2. As illustrated in FIG. 10, the eNB 200-2 transmits thesynchronization signal 2, in the cell 2 using the subcarrier spacing of30 kHz. The eNB 200-2 applies the subcarrier spacing of 15 kHz to thetime location for transmitting the synchronization signal 2. Further,the eNB 200-2 arranges the synchronization signal 2 into the previouslyset time location.

The UE 100 uses 15 kHz or previously set specified subcarrier spacing toperform the reception process of the synchronization signal 2(synchronization process) at the previously set time location. Then, theUE 100 recognizes, based on the signal sequence of the receivedsynchronization signal 2, the subcarrier spacing (30 kHz) of the cell 2.After recognizing the subcarrier spacing of the cell 2, the UE 100performs the reception process of another signal of the cell 2 by usingthe subcarrier spacing. The UE 100 can start communication with the cell2 by receiving these signals.

(2) Summary of Second Embodiment

According to the second embodiment, the eNB 200 applies the subcarrierspacing (15 kHz or specified subcarrier spacing) different from theother time location (that is, the subcarrier for transmitting the data),only to the time location of the synchronization signal. As a result,with a standardized synchronization process, the UE 100 can receive thesynchronization signal of each cell. Therefore, even if the subcarrierspacing is scalable, it is possible to suppress an increase of a processload of the UE 100.

Third Embodiment

A third embodiment will be described while focusing on differences fromthe first, second embodiments, below. An assumed scenario according tothe third embodiment is similar to the assumed scenario according to thefirst embodiment.

(1) Operation According to Third Embodiment

The eNB 200 according to the third embodiment includes a transmitter 210configured to transmit, in the first cell, subcarrier spacinginformation, to the UE 100. The subcarrier spacing information indicatesthe subcarrier spacing of the second cell different from the first cell.The first cell may be a primary cell (PCell) of the UE 100 and thesecond cell may be a secondary cell (SCell) of the UE 100. The PCell maybe a cell similar to an existing LTE cell, and the SCell may be a cellof the 5G mobile communication system.

The UE 100 according to the third embodiment includes a receiver 110configured to receive, in the first cell, the subcarrier spacinginformation from the eNB 200, and a controller 230 configured torecognize, based on the subcarrier spacing information, the subcarrierspacing of the second cell. The controller 230 performs the receptionprocess of the synchronization signal of the second cell by using therecognized subcarrier spacing.

FIG. 11 is a chart illustrating an operation example of the eNB 200 andthe UE 100 according to the third embodiment. Here, an example isillustrated where the first cell (PCell) and the second cell (SCell) aremanaged by the same eNB 200. In the example of FIG. 11, the subcarrierspacing of the first cell (PCell) is 15 kHz and the subcarrier spacingof the second cell (SCell) is 30 kHz. In an initial state of FIG. 11,the UE 100 has a connection with the first cell (PCell), but does nothave a connection with the second cell (SCell).

As illustrated in FIG. 11, in step S11, the eNB 200 transmits, in thefirst cell (PCell), measurement configuration information (MeasurementConfig) including the subcarrier spacing information indicating thesubcarrier spacing of the second cell (SCell), to the UE 100. Themeasurement configuration information is transmitted by a dedicated RRCsignaling. However, the measurement configuration information may betransmitted by a broadcast signaling. The measurement configurationinformation may include not only the subcarrier spacing information butalso information indicating a center frequency of the second cell(SCell). Further, the measurement configuration information may includeinformation indicating a service (that is, use of the cell 2) providedby the second cell (SCell).

In step S12, the UE 100 starts, based on the received measurementconfiguration information, the measurement on the second cell (SCell).Here, the UE 100 recognizes the subcarrier spacing of the second cell(SCell), based on the subcarrier spacing information included in themeasurement configuration information.

In step S13, the eNB 200 transmits, in the second cell (SCell), thesynchronization signal. The UE 100 uses the subcarrier spacingrecognized in step S12 to perform the reception process of thesynchronization signal of the second cell (SCell).

Thereafter, the UE 100 performs the measurement on the reference signaland the like of the second cell (SCell), and transmits the measurementresult to the first cell (PCell). The eNB 200 transmits, based on themeasurement result, configuration information for adding the second cellas the SCell, to the UE 100. Accordingly, the UE 100 performs a carrieraggregation simultaneously using the first cell (PCell) and the secondcell (SCell).

(2) Summary of Second Embodiment

According to the third embodiment, one cell previously notifies the UE100 of the subcarrier spacing of another cell. As a result, the UE 100can easily receive the synchronization signal of the other cell.Therefore, even if the subcarrier spacing is scalable, it is possible tosuppress an increase of a process load of the UE 100.

(3) Modification of Third Embodiment

In the third embodiment described above, an example was described wherethe subcarrier spacing information is transmitted from the first cell(PCell) to the UE 100 by the dedicated signaling. However, thesubcarrier spacing information may be transmitted by the broadcastsignaling from the first cell (PCell). Further, the subcarrier spacinginformation may be a list of the subcarrier spacings of a plurality ofcells. The list includes a plurality of entries, and each entry mayinclude an identifier of a cell and the subcarrier spacing of the cell.

Further, in the third embodiment described above, an example wasdescribed where the first cell and the second cell are managed by thesame eNB 200. However, the first cell may be managed by the eNB 200-1and the second cell may be managed by the eNB 200-2. In this case,instead of the carrier aggregation, a Dual connectivity may beperformed. In the Dual connectivity, the second cell may be referred toas “primary secondary cell (PSCell)”. Further, prior to the sequence ofFIG. 11, the eNB 200-2 may notify the eNB 200-1, via a backhaul, of thesubcarrier spacing of the cell 2. For example, the eNB 200-2 notifiesthe eNB 200-1, on the X2 interface or the S1 interface, of thesubcarrier spacing of the cell 2.

Other Embodiments

Each of the above-described first to third embodiments may be performedindividually and may also be performed by combining two or more of theembodiments.

In the embodiments described above, it was assumed that the 5G mobilecommunication system is a system evolved from the LTE system. However,the 5G mobile communication system includes the LTE and a new radioaccess technology (new RAT). The present invention may be applied to amobile communication system where such a new radio access technology isused.

[Appendant]

(11) A base station, comprising: a transmitter configured to transmit,in a first cell, subcarrier spacing information to a radio terminal,wherein

the subcarrier spacing information indicates a subcarrier spacing of asecond cell different from the first cell.

(12) The base station according to (11), wherein the first cell is aprimary cell of the radio terminal, and

the second cell is a secondary cell of the radio terminal.

(13) A radio terminal, comprising: a receiver configured to receive, inthe first cell, subcarrier spacing information from a base station,where the subcarrier spacing information indicates a subcarrier spacingof a second cell different from the first cell; and

a controller configured to recognize, based on the subcarrier spacinginformation, the subcarrier spacing of the second cell.

(14) The radio terminal according to claim 13, wherein the controllerperforms a reception process of a synchronization signal of the secondcell by using the recognized subcarrier spacing.

INDUSTRIAL APPLICABILITY

The present invention is useful in the field of radio communication.

1. A base station, comprising: a transmitter configured to transmit userdata in a cell using a predetermined subcarrier spacing, the cell beingmanaged by the base station; and a controller, wherein the transmitteris configured to transmit a synchronization signal in the cell, and thecontroller is configured to apply a subcarrier spacing different fromthe predetermined subcarrier spacing to a time location for transmittingthe synchronization signal.
 2. The base station according to claim 1,wherein if the predetermined subcarrier spacing is different from apreviously set specified subcarrier spacing, the controller applies thespecified subcarrier spacing to a time location for transmitting thesynchronization signal.
 3. The base station according to claim 2,wherein the specified subcarrier spacing is a subcarrier spacing used bya radio terminal for a reception process of the synchronization signal.4. The base station of claim 1, wherein the synchronization signalincludes a signal sequence indicating the predetermined subcarrierspacing.
 5. A base station, comprising: a transmitter configured totransmit a synchronization signal in a cell using a predeterminedsubcarrier spacing, the cell being managed by the base station; and acontroller configured to arrange, based on the predetermined subcarrierspacing, the synchronization signal in a plurality of discretesubcarriers not continuous in a frequency direction.
 6. The base stationaccording to claim 5, wherein the controller is configured to arrangethe synchronization signal in the plurality of discrete subcarriers, ifthe predetermined subcarrier spacing is narrower than a previously setspecified subcarrier spacing, and in the plurality of discretesubcarriers, a spacing between the two adjacent discrete subcarriers isequal to the specified subcarrier spacing.
 7. The base station accordingto claim 6, wherein the specified subcarrier spacing is a subcarrierspacing used by a radio terminal for a reception process of thesynchronization signal.
 8. The base station of claim 1, wherein thesynchronization signal includes a signal sequence indicating thepredetermined subcarrier spacing.
 9. A radio terminal, comprising: areceiver configured to receive a synchronization signal of a cell of abase station; and a controller configured to perform a reception processof the synchronization signal by using a previously set specifiedsubcarrier spacing, irrespective of a subcarrier spacing of the cell.10. The radio terminal according to claim 9, wherein the synchronizationsignal includes a signal sequence indicating a subcarrier spacing of thecell, and the controller recognizes, based on the signal sequence, thesubcarrier spacing of the cell.